DE19950902A1 - System and method for controlling a positioning device, in particular actuators in machine tools, and a phase mixing device - Google Patents

Abstract

The invention relates to a system in order to control a positioning device, in particular positioning devices for tool machines, whereby said system comprises an incremental position measuring device with an output signal having a sin phi 1, sin ( phi 1 +/- p) form and a control unit which converts an output signal into a control signal and thereby control said positioning device. Means are provided for adding in a correction angle phi 2 to the output signal. Said means are placed between the positioning device and the control unit such that the output signal obtained has the form of a sin ( phi 1 +/- phi 2), sin ( phi 1 +/- phi 2 +/- p) prior to conversion to a control signal in the control unit.

Description

The invention relates to a system and a method for controlling a positioning device, in particular actuators in machine tools, with an incremental position measuring device with output signals of the form sinϕ ₁ , sin (ϕ ₁ ± p) and a control unit converting the output signals into control signals and thus controlling the positioning device . P is an angle by which the two output signals are out of phase.

The invention further relates to a phase mixing device, which in the said system or the implementation of said method can be used.

For machine tools, processing and manufacturing machines, but also for various measuring and Test equipment it is necessary to have a tool or a probe relative to a workpiece or automatically position a part to be checked. For the sake of simplicity, the Invention in the following always using the example of the positioning of a tool Machine tool described relative to a workpiece, but without the invention this special application would be limited.

For the positioning of tools and workpieces, the tools are modern Machine tools as a rule can be moved and pivoted or pivoted around five or more axes rotatable. The traversing and swiveling or rotating movements are controlled by a central one  Control unit, usually a so-called numerical control (NC) controlled, the Control unit from a position measuring device when moving, pivoting or rotating continuously receives information about the position changes made.

The so-called incremental (counting) Position measuring systems have proven particularly successful. A distinction is made between the type of output signals thereby between measuring devices with rectangular (and thus quasi digitized) Output signals (whereby the signals are usually transmitted in the form of a voltage pulse ) and those with sinusoidal (i.e. analog) output signals. The facilities with Rectangular output signals are characterized by a relatively simple Signal processing off, with positional deviations usually ± 3% of the signal period be.

Should with a relatively short sampling time of z. B. 250 µs travel speeds of at least 0.01 m / min, and should be at least a change for reasons of accuracy one measuring step per scanning cycle, a measuring step of only 0.04 µm is required. With this measuring step, z. B. at 60 m / min a step frequency of 60 m / (60 s. 0.04 µm) = 25 MHz. In order to keep the circuit complexity in the subsequent electronics low, To strive for input frequencies less than 1 MHz. For such high travel speeds and Very small measuring steps have become incremental position measuring devices with sinusoidal Output signals have been tried and tested with a relative position deviation within a Signal period for drives with digital speed control of less than 1% of the respective Signal period of the measuring device are even more accurate than measuring devices with rectangular Output signals.

Now there is the problem that due to non-linearities, thermal expansion, Vibrations etc. Workpiece and tool are actually in one position relative to each other  are located, which deviates from the position, which the control unit due to it from the Measuring device has calculated signals transmitted. Although such deviations are often very limited are low, they can be used in cases where extremely low manufacturing tolerances Machining a workpiece are given lead to the entire workpiece becomes unusable. These are under certain conditions and / or in certain positions Any deviations that occur can often be calculated or measured beforehand.

Proceeding from this, the object of the invention is a device and a method for Control of a positioning device to specify in which certain position deviations can be automatically taken into account without changes to the itself proven control units or their mode of operation would have to be carried out.

The object is achieved by a system of the type mentioned at the outset, in which means for mixing a correction angle ϕ ₂ into the output signals are provided and are connected between the position measuring device and the control unit in such a way that the output signals have the form sin (ϕ ₁ ± ϕ ₂ ), sin (ϕ ₁ ± p ± ϕ ₂ ) before they are converted into control signals by the control unit.

The invention is therefore based on the basic idea of "intercepting" the position signals supplied by the respective position measuring device on their way to the control unit, changing them according to predetermined criteria and supplying the changed position signals to the control unit, in order in this way to deviate between the measured and the actual position of the to be controlled tool or the like. The correction angle ϕ _{2 to} be mixed in can - depending on the type of positioning device to be controlled and depending on the particular characteristics - also be far greater than 2π or 360 °, so that not only deviations within a step interval, but also deviations due to the correction angle any size can be corrected. The correction angle can thus theoretically even be used to control the positioning device.

The correction angle itself can be determined in a variety of ways, some of which are known and which are not the subject of this application. For example, the correction angle ϕ ₂ during out-of-round machining can be a function f (x, y) of the measured out-of-roundness of the surface to be machined. With volumetric compensation, ϕ ₂ can be a function of one or more other functions, e.g. B. a function of temperature, axis expansion, etc.

The invention has the great advantage that due to the fact that on the control unit itself No interventions are required, even finished machines can be easily retrofitted or can be converted to the new control method.

In a preferred embodiment of the invention, the means for mixing in a correction angle ϕ ₂ comprise an analog phase mixer. The latter can access at least one, preferably two, freely programmable correction angle tables with values of the correction angles ϕ ₂ to be taken into account for certain states x or their trigonometric equivalents, so that the correction angle ϕ _{2 is} not a constant value, but rather one of one or more parameters. such as B. pressure, temperature, absolute position etc. - dependent function f (x) of the state x, i.e. ϕ ₂ = f (x). Certain output signals of the position measuring device and certain intervals of ϕ ₁ can also be assigned certain correction angles ϕ ₂ . So z. B. be provided to divide the values of reich ₁ from 0 to 2π or 0 ° to 360 ° into 1024 intervals and to assign a value ϕ ₂ to each interval.

In an advantageous development of the invention, which is characterized by particularly quickly determining the corrected values sin (ϕ ₁ ± ϕ ₂ ), sin (ϕ ₁ ± ϕ ₂ ± p) to be supplied to the control unit, the analog phase mixer has four multiplying A / D Converter, wherein one converter is switched to generate one of the following four values: sinϕ ₁ . cosϕ ₂ , cosϕ ₁ . sinϕ ₂ , sin (ϕ ₁ ± p). cosϕ ₂ , cos (ϕ ₁ ± p). sinϕ ₂ . If the phase shift p between the output signals is exactly 90 °, which is usually the case, sin (ϕ ₁ ± p) corresponds to cosϕ ₁ and the output signals thus have the form sinϕ ₁ , cosϕ _1, so the converters can be used to form the values cosϕ _1st sinϕ ₂ , sinϕ ₁ . sinϕ ₂ , sinϕ ₁ . cosϕ ₂ and cosϕ ₁ . cosϕ _{2 be} switched.

It has proven to be expedient if the analog phase mixer has two adding amplifiers, each of which has the values sin (ϕ ₁ ± ϕ ₂ ), sin (ϕ ₁ ± ϕ ₂ ± p) from the output values of two A / D converters. form. The adder amplifiers then advantageously allow the output signals from the phase mixer to the control unit to be shaped, possibly with the interposition of a filter, so that their characteristics correspond exactly to the output signals supplied by the position measuring device, the reception of which the control unit is usually set and optimized.

Alternatively, it can also be provided that the means for mixing in the correction angle ϕ2 at least one A / D converter for converting the analog output signals of the form sinϕ ₁ , sin (ϕ ₁ ± p) of the incremental position measuring device into digital signals and a digital arithmetic unit for the calculation of the values sin (ϕ ₁ ± ϕ ₂ ), sin (ϕ ₁ ± p ± ϕ ₂ ), the digital computing unit then having access to at least one, preferably two freely programmable correction angle tables in which the values of the to be determined States x correction angle ϕ ₂ to be taken into account or their trigonometric equivalents, in particular the values sinϕ ₂ and sin (ϕ ₂ ± p) are stored.

The above object is further achieved by a method for controlling a positioning device, in particular actuators in machine tools, output signals of the form sinϕ ₁ , sin (ϕ ₁ ± p) being generated by an incremental position measuring device and being fed to a control unit which sends the output signals into the converts a positioning device to control signals, the correction signals vor _{2 being} added to the output signals upstream of the supply to the control unit such that the output signals are given the form sin (ϕ ₁ ± ϕ ₂ ), sin (ϕ ₁ ± p ₂ ± p).

The method can be carried out in such a way that the addition of the correction angle ϕ ₂ when converting the analog output signals of the form sin Form ₁ , sin (ϕ ₁ ± p) of the incremental position measuring device into digital signals, preferably using one or more multiplying A / D- Converter takes place, this procedure ensures a particularly fast and also suitable for high input frequency signal processing.

Alternatively, the method may e.g. B. be carried out so that the admixing of the correction angle ϕ ₂ after the conversion of the analog output signals of the form sinϕ ₁ , sin (ϕ ₁ ± p) of the incremental position measuring device into digital signals is preferably carried out using a digital computing unit.

To implement the system and method according to the invention, a phase mixing device (hereinafter referred to as phase mixer for short) for mixing in a correction angle ϕ ₂ into the sinusoidal output signals sinϕ ₁ , sin (ϕ ₁ ± p) of incremental position measuring devices is proposed, which means for reading in the output signals sinϕ ₁ , sin (ϕ ₁ ± p) from the position measuring device, a memory device for storing at least one table with correction angles ϕ2 to be taken into account in state x or trigonometric equivalents of these angles, four multiplying A / D converters to form two according to the addition theories for the sums / differences Angle to be taken into account and two adding amplifiers connected to two of the multiplying A / D converters to form the values sin (ϕ ₁ ± ϕ ₂ ) and sin (ϕ ₁ ± ϕ ₂ ± p) from those of the multiplying A / D- Transducers delivered values includes.

Alternatively, the phase mixing device can also be designed in such a way that it provides a means for reading analog sinusoidal output signals sinignale ₁ , sin (ϕ ₁ ± p) of an incremental position measuring device, a memory device for storing at least one table with correction angles ϕ ₂ to be taken into account in state x or trigonometric equivalents this angle, at least one A / D converter for converting the sinusoidal analog output signals into digital signals and a digital arithmetic unit for forming the values sin (ϕ ₁ ± ϕ ₂ ) and sin (ϕ ± p ₁ ± ϕ ₂ ) or cos ( ϕ ₁ ± ϕ ₂ ) from the digital signals supplied by the at least one A / D converter.

Further details and advantages of the invention emerge from the following description some embodiments in connection with the drawing. Show it:

Fig. 1 is a schematic diagram for explaining the issue, that is, the interference sinφ a correction angle φ ₂ into the output signals of the form _1, cos ₁ (with a phase shift of p 90 °),

Figs. 2 and 3 is a block diagram of a phase blending gate with an analogue phase mixer,

Fig. 4 is a greatly simplified schematic diagram of the integration of the analogue phase mixer in an encoder interface,

Fig. 5 is a circuit diagram of the analogue phase mixer with four multiplying A / D converters and two addition amplifiers,

Fig. 6 is a diagram of the actuation of the phase mixer,

Fig. 7 is a limitation to the maximum possible output frequency of analog low-pass filter connected downstream of the phase mixer,

Fig. 8 is a block diagram of the output stage for amplifying the low-pass filtered analog signal,

Fig. 9 is a block diagram of the encoder evaluation means MIP-blocks,

Fig. 10 is a schematic diagram to illustrate the typical waveform of the interpolated signal sequences and

Fig. 11 is a schematic representation of the basic principle in the generation of reference signals

In Fig. 1 is shown schematically how the known by a per se and behave position measuring supplied sinusoidal output signals therefore not further illustrated here, the phase offset between the two output signals of exactly 90 °, so that, therefore, the signal sine the other signal changes cosine. In the known controls would now position z from the values sinϕ ₁ and cosϕ ₁ . B. determined a tool on a machine tool. As stated above, there is the problem that, due to various circumstances, the measured position does not match the actual one.

While correction values can be added or subtracted relatively easily to the measured values in the case of known position errors in digital position measuring devices, this is not readily possible in the case of principally more precise measuring systems with sinusoidal output signals. According to the invention, it is now provided to correct deviations by mixing in a correction angle ϕ ₂ in the output signals, so that the values sin ϕ ₁ and cos ϕ ₁ used by a control unit for controlling a positioning device change according to the addition theories for the sum or difference of two angles. For nontrivial mixing of such a correction angle φ ₂ serving phase blending gate with an analogue phase mixer, Figs. 2 and 3, with FIG. 3, FIG. 2 does not continue the block diagram of a scale.

The phase mixer gate shown in FIGS . 2 and 3 is divided into the following areas:

• - Input circuit for encoder including error decoding and external 24 volt signal, whereby can optionally be provided that a non-isolated AC-DC converter connected measuring system supplied with voltage,
• - analog phase mixer and analog reference signal generation,
• - digitization of the sinusoidal input-output signals,
• - output circuit as encoder simulation for subsequent controls,
• - FPGA (Field Programmable Gate Array) with oscillator, in which it is freely programmable Hardware the actual phase mixer gate functions are implemented,
• - Plug & Play controller, whereby this module acts as a link to the ISA-BUS Address decoding of the phase mixing gate and the interrupt capability delivers and that Phase mixer gate due to the P&P capability also for modern, future boards with new BI OS versions and operating systems is suitable and configuration in an internal EEPROM is
• - data and address buffers for decoupling the card from ISA-BUS,
• - A flash EPROM containing the bit map of the FPGA module, the content of which after Switching on is automatically transferred to the FPGA within a few milliseconds FPGA is working.

The main function of the phase mixer gate shown is to supply measuring system signals "falsify", namely the subsequent control by mixing in a targeted number of  To transmit path increments a different position information than from the actual one Position measuring device determined. This mixing process can be used for a wide variety of machines and Devices are used, especially in the so-called volumetric compensation, non-circular machining and temperature compensation.

The phase mixer gate shown in FIGS . 2 and 3 is able to generate a sinusoidal reference signal from the sine-cosine signals of the encoder in the cases in which a measuring system without its own zero pulse must be used, this process by a external reference switch is initiated and installed in the next possible analog signal grid (see FIG. II). As shown in FIG. 10, the reference marks generated by the interpolator lie exactly in the grid of the path signals according to the rules for digital measuring systems, this being true both for the signals for the division ratio of 1 and for the signals with interpolated signal sequences.

FIG. 4 shows a schematic diagram of a transducer interface which consists of two encoder inputs with interpolators, one of which can be optionally used as the second sensor input. A simulated encoder output can either forward the input signals of the optional input or the encoder signals generated in the phase mixer gate to the subsequent control. With the second interpolator, the sum of the mixed signal and encoder input is recorded separately and fed to the FPGA.

The heart of the system according to the invention is an analog phase mixer, in which the analog signals of the position measuring device with the angle ϕ ₁ are shifted by an angle ϕ ₂ with a defined frequency, this being the same for both values sinϕ ₁ and sin (ϕ ₁ ± p) he follows. Since the phase shift p between the two signals is usually exactly 90 °, the signal sin (ϕ ₁ ± p) corresponds to the value cosϕ ₁ . Depending on the application, the invention allows the angle ϕ ₁ to be increased or decreased by a correction angle Anwendungs ₂ . In the circuit shown in FIG. 5, it was assumed that the correction angle ϕ ₂ should be drawn from the value of the value ϕ ₁ . Accordingly, the circuit must automatically output signals sinϕ ₁ , cosϕ _{1 of} the position measuring device, which form the input signals of the phase mixer, into the output signals sin (ϕ ₁ - ϕ ₂ ) and cos (ϕ ₁ - ϕ ₂ ) to be fed to the control unit (not shown here). convert. This is done using the relationships sin (ϕ ₁ - ϕ ₂ ) = sinϕ ₁ . cosϕ ₂ - cosϕ ₁ . sinϕ ₂ and cos (ϕ ₁ - ϕ ₂ ) = cosϕ ₁ . cosϕ ₂ + sinϕ ₁ . sinϕ ₂ . The individual multiplication terms are generated in four stages. The input signals symmetrical to 0 V form the angle ϕ ₁ . The angles ϕ _{2 of} the mixing process are generated by sine-cosine tables. These tables are controlled by EPROMS from the FPGA and the "mixed frequency" generated therein. The resolution is z. B. 10 bits for a full circle. Four multiplying A / D converters form the individual stages of the individual results, which are then calculated by adding amplifiers. The circuit shown is fully static, so that intermediate results are advantageously retained.

The phase mixer shown in FIG. 5 is controlled as shown in FIG. 6. The pulses E2 + / and E2i generated in the generation of the mixed angle are recorded in a bidirectional buffer counter of 10 bits in this exemplary embodiment. These 10 bits represent a circle with 1024 partial angles, each of which is assigned a value in the sine-cosine EPROM tables. With each new pulse E2i, a sequence is initiated with which the new angle value is transferred to the A / D converter via the EPROM tables. If you want to get different loop resolutions, so that you can work with high sampling frequencies, several tables in the loop resolutions 10 bit (= 2π / 1024), 9 bit (= 2π / 512), 8 bit (= 2p / 256) and 7 bits (= 2π / 128) can be realized.

FIG. 7 shows a low-pass filter, specifically a three-pole Bessel filter, with which it is advantageously possible to limit the maximum possible analog output frequencies of the phase mixer. The cut-off frequency is approximately 300 kHz.

In FIG. 8, an initial stage is shown, which amplifies the analog signal from the internal processing stages of the phase mixer, and the inverted signal with the same specifications as the signal received by the phase mixer output signals of the position measuring device has. A correction voltage raises the zero point of the analog signal level back to the normal level between 0 and 5 volts, which advantageously has the result that the control unit connected downstream detects no difference from a direct measuring system output.

The analog measuring system signal is evaluated by means of interpolator components, as shown in FIG. 9. The modules are able to break down the circle formed by the sine and cosine signals into uniform angle segments and thus achieve a selectable multiplication of the encoder signals up to a factor of 50. The signals generated are in digital form and are Gray-coded, corresponding to a one-step code. The block supplies the signals in parallel. 1 and the interpolated signals that can be selected via two inputs.

Within the framework of the inventive concept, numerous modifications and further developments are possible, which are e.g. B. refer to the circuit implementation of the phase mixer. Essential to the invention is in any case the admixing of any error-correcting and - if desired - also deliberately used to control certain positions serving correction angle in the position signals supplied by a position measuring device on their way to the control unit, the admixing preferably using the addition theorems for the addition of two angles (sin (ϕ ₁ ± ϕ ₂ ) = sinϕ _1. cosϕ ₂ ± cosϕ _1. sinϕ ₂ , cos (ϕ ₁ ± ϕ ₂ ), = cosϕ _1. cosϕ ₂ ± sinϕ _1. cosϕ ₂ ).

Claims (15)

1. System for controlling a positioning device, in particular actuators in machine tools, with an incremental position measuring device with output signals of the form sinϕ ₁ , sin (ϕ ₁ ± p) and a control unit converting the output signals into control signals and thus controlling a positioning device, characterized in that Means for mixing a correction angle ϕ ₂ into the output signals are provided and connected between the position measuring device and the control unit in such a way that the output signals are given the form sin (ϕ ₁ ± ϕ ₂ ), sin (ϕ ₁ ± ϕ ₂ ± p) before they are converted into control signals by the control unit. 2. System according to claim 1, characterized in that the means an analog Include phase mixers. 3. System according to claim 2, characterized in that the phase mixer can access at least one freely programmable correction angle table with values of the correction angles ϕ ₂ to be taken into account for certain states x or their trigonometric equivalents. 4. System according to claim 3, characterized in that the phase mixer can access two correction angle tables in which the values to be considered for certain states x sinϕ ₂ and sin (ϕ ₁ ± ϕ ₂ ) are stored. 5. System according to claim 4, characterized in that the analog phase mixer has four multiplying A / D converters, one converter being connected to generate one of the following four values: sinϕ ₁ . cosϕ ₂ , cosϕ ₁ . sinϕ ₂ , sin (ϕ ₁ ± p). cos (ϕ ₂ ± p), cos (ϕ ₁ ± p). sin (ϕ ₂ ± p). 6. System according to claim 4, wherein the phase shift p between the output signals is 90 °, the output signals thus have the form sinϕ ₁ , cosϕ ₁ , characterized in that the analog phase mixer has four multiplying A / D converters, one each Converter for forming one of the values cosϕ ₁ . sinϕ ₂ , sinϕ ₁ . sinϕ ₂ , sinϕ ₁ . cosϕ ₂ and cosϕ ₁ . cosϕ _{2 is} switched. 7. System according to claim 5 or claim 6, characterized in that the analog phase mixer has two adder amplifiers, each of the output values of two A / D converters one of the values sin (ϕ ₁ ± ϕ ₂ ), sin (ϕ ₁ ± ϕ ₂ ± p) or cos (ϕ ₁ ± ϕ ₂ ). 8. System according to claim 1, characterized in that the means for mixing in the correction angle ϕ ₂ at least one A / D converter for converting the analog output signals of the form sinϕ ₁ , sin (ϕ ₁ ± p) of the incremental position measuring device in digital signals and a digital arithmetic unit for calculating the values sin (ϕ ₁ ± ϕ ₂ ), sin (ϕ ₁ ± p ± ϕ ₂ ). 9. System according to claim 8, characterized in that the digital computing unit can access at least one freely programmable correction angle table with values of the correction angles ϕ ₂ to be taken into account for certain states x or their trigonometric equivalents. 10. System according to claim 8, characterized in that the digital arithmetic unit can access two correction angle tables in which the values sinϕ ₂ and sin (ϕ ₂ ± p) to be taken into account for certain states x are stored. 11. Method for controlling a positioning device, in particular actuator drives in machine tools, output signals of the form sinϕ ₁ , sin (ϕ ₁ ± p) being generated by an incremental position measuring device and being fed to a control unit which converts the output signals into the control signals controlling a positioning device, characterized in that correction angles vor ₂ are added to the output signals before being fed to the control unit in such a way that the output signals are given the form sin (ϕ ₁ ± ϕ ₂ ), sin (ϕ ₁ ± ϕ ₂ ± p). 12. The method according to claim 11, characterized in that the admixing of the correction angle ϕ ₂ in the conversion of analog output signals of the form sinϕ ₁ , sin (ϕ ₁ ± p) of the incremental position measuring device into digital signals, preferably using one or more multiplying A / D -Converters done. 13. The method according to claim 11, characterized in that the admixing of the correction angle ϕ ₂ after the conversion of analog output signals of the form sinϕ ₁ , sin (ϕ ₁ ± p) of the incremental position measuring device into digital signals is preferably carried out using a digital computing unit. 14. Phase mixing device for mixing in a correction angle ϕ ₂ into sinusoidal output signals sinϕ ₁ , sin (ϕ ₁ ± p) of an incremental position measuring device, comprising

• Means for reading in the output signals sinignale ₁ , sin (ϕ ₁ ± p),
• a storage device for storing at least one table with correction angles ϕ ₂ to be taken into account in state x or trigonometric equivalents of these angles,
• - Four multiplying A / D converters to form terms to be taken into account in accordance with the addition toremes for the sum of two angles and
• - Two adding amplifiers connected to two of the four multiplying A / D converters to form the values sin (ϕ ₁ ± ϕ ₂ ) and sin (ϕ ₁ ± ϕ ₂ ± p) or cos (ϕ ₁ ± ϕ ₂ ) from the from the multiplying A / D converters.

15. Phase mixing device for mixing in a correction angle ϕ ₂ into analog sinusoidal output signals sinϕ ₁ , sin (ϕ ₁ ± p) of an incremental position measuring device, comprising

• Means for reading the analog output signals sin Ausgangss ₁ , sin (ϕ ₁ ± p),
• a storage device for storing at least one table with correction angles ϕ ₂ to be taken into account in state x or trigonometric equivalents of these angles,
• - At least one A / D converter for converting the sinusoidal analog output signals into digital signals and
• - A digital arithmetic unit for forming the values sin (ϕ ₁ ± ϕ ₂ ) and sin (ϕ ₁ ± p ₁ ± ϕ ₂ ) or cos (ϕ1 ± ϕ ₂ ) from the digital supplied by the at least one A / D converter Signals.